There is not any artificial valve implantable remotely by catheter for use in blood vessels available up to the present day.
Moreover, there is not any artificial valve for use in veins commercially available up to the present day, notwithstanding some specific attempts, such as those valves disclosed by Lane (International Application Number PCT/AU87/00220), Taheri (International Application Number PCT/US88/03175) and Quijano et al. (PCT/US90/03053).
The main problem with such valves is the ease of thrombosis, which immobilizes the valve and, therefore, prevents it from operating,
More specifically, Lane's valve is not, strictly speaking, a valve, but only an outer prosthesis whereinto a vein segment is intussuscepted to form a venous valve, in which the blood does not come in contact with the prosthesis itself. It is not commercially available, and it is not implantable remotely by a catheter.
Taheri's valve has an annular support which has a tendency to go out of alignment when implanted in a vein during low endoluminal pressure stages and when the vein is compressed From the outside. Its valving means are two leaflets, which are not protected by the annular support during their motion of opening and closing from the collapse of the venous wall during low endoluminal pressure stages and when the vein is compressed from the outside. It is not commercially available, it is not implantable remotely by a catheter.
Quijano et al.'s valve is a biological valve, i.e. it is entirely made from animal tissues, and has a two-leaflet valving means. It is not commercially available, and it is not implantable remotely by a catheter.
Various types of artificial valves made for use in hearts (i.e. heart valves) are known in the operative art: these valves are not applicable in veins. In fact, they are intrinsically different from venous valves various reasons, e.g. structure, size, materials or the characteristics of mechanical strength the forces necessary for their operation, the way of insertion, or the method fop fixing them in the desired site. In the heart and in the vessels connected therewith, there are high pressures and high instantaneous flows; moreover, the vessels have large diameters and are protected against compression from the outside by virtue of being positioned inside the thorax. On the contrary, in veins there are low pressures and low flows; moreover, the diameters of the veins that have valvular incompetence are small and these veins are easily compressible from outside under various conditions.
In order to provide an artificial valve that could operate in a vein, the same Applicant hereof suggested in Italian Patent Application Ser. No. RM91A000458 on the 25.sup.th Jun., 1991, a valve configured to allow unidirectional flow, biocompatible with veins, comprising
a hollow elongated support having a predetermined length with a periphery and a predetermined width, said length being greater than said width, said support having means for fixing itself to a vein, and PA1 a plate carried by and within the support and movable relative to the support between a first position to allow flow of blood in one direction and a second position to prevent flow of blood in an opposite direction through said support, PA1 said plate being disposed entirely within said support in both of said first and second positions.
Such a valve has only one valving element, as this is made up of the plate, which is a monocusp; so thrombogenesis is substantially reduced and the valve is able to operate reliably.
The fact that the valving element is always inside said support during its motion ensures that it is always protected against the collapse of the vein during low pressure stages.
The main object of the present invention is to provide a valve for use in blood vessels, which is implantable remotely by catheter.
Another object of the present invention is to provide a valve for use in blood vessels, which is substantially less thrombogenic than the known ones.
Such objects are achieved, according to the teaching of the present invention, by utilizing a suitably bent flexible wire having elasticity and plasticity as the support of the valving means.
As used herein "having elasticity and plasticity" means that said wire is plastically de formed when twisted into turns by an operator, but reacts elastically to the forces applied to it by the wall of a blood vessel, particularly a vein, once implanted in the blood vessel itself.
The advantages offered by the present invention are mainly that it provides a valve for use in blood vessels and that is implantable remotely by catheter, which was never done before. This advantage is achieved by virtue of the cage structure of the wire support, which can be so made, as to be folded in such a way as to free its three-dimensional space occupation. After introduction at a remote distance, percutaneously, of the valve into the desired site, the valve itself can be restored to its original three-dimensional configuration.
Moreover, the present invention affords a valve which is substantially less thrombogenic than the known ones: indeed, its support does not develop bidimensionally, by virtue of its cage structure; then it offers a very restricted extension for the formation of thrombi.